Any triskadecaphobics out there may be slightly disturbed to learn that this is numero 13 in this series of glimpses into the exotic wonders of dart flight dynamics. But that doesn’t seem to have affected my luck too badly because I’ve had a bit of a result.
My distinctly unexotic plan for this particular offering had been to look at why the flights on Sigma darts have what aerodynamicists call a delta planform and everybody else calls a kite shape. Unfortunately this plan had one drawback that I hadn’t quite resolved. Explain things too simplistically and I might disappoint my more technically inclined readers like Chris R and Bob. Provide a full technical dissertation, on the other hand, and, at the first mention of a “lift coefficient maxima”, most of my audience would probably decide to entertain themselves by reading Dartoid instead.
Luckily, Red has solved this dilemma for me. By putting in a comment to my last blog full of phrases like “linearized theory” and “separation vortices”, he has saved me from having to mention anything of the sort. So now anyone who wants to delve further into the intricacies of delta wing aerodynamics can just read Red’s post (and Red can award himself his small prize!) whilst I sit back and provide a more relaxed overview, which handily leaves more room for the usual Q&As at the end.
And my first relaxed overview point is that, although delta flights might look very aerodynamic, they’re in fact normally not that efficient at generating lift, which is why nearly all non-military aircraft don’t have delta wings. They’re good supersonically, hence Concorde and modern jet fighters have them, but that isn’t of much relevance to a dart player (unless, maybe, he wears blue lycra and is allergic to Kryptonite).
However, although delta flights might not generate as much lift as normal shaped flights, they do keep generating it to a higher yaw angle. That’s why Concorde had that “droop snoop”, it came in to land nice and slowly at an angle which could have caused a normal plane to stall – which was great except that the pilot wouldn’t have been able see the runway if the nose hadn’t been able to tilt forward.
And that high stall angle, the mechanism for which Red has so helpfully pretty much explained, is important for Sigma darts because stalling could ruin those carefully crafted yaw wavelengths that give the benefits I’ve described in previous blogs.
Because Sigma Ones are intended to be more stable and have more yaw damping than Sigma Pros, they need more lift from their flights. A full delta shape with enough area to generate the required amount of lift would be so long and wide at the back players would be in danger of poking themselves in the eye when throwing, so the Sigma One flight is a compromise which Unicorn have called an “enhanced delta”. It has more-or-less the same length and width (“span” in aerodynamics-speak) as a standard “Plus” flight, but still enough sweep-back angle on the leading edge to help prevent stalling.
Sigma Pros, which don’t need so much lift, can use a much smaller flight, meaning a full delta shape can be used. One consequence of this is that the tip of the flights is very pointed, making them weak at the front and hence slightly more suited to side-load than end-load shafts. So, as with most aspects to the design of Sigmas, there is a scientific reason for what might have seemed like this arbitrary choice of shaft type!
Finally, although I suspect not many perusing this blog will have had occasion to read the Scottish edition of the Sun newspaper on April 1st, if you did happen to I would just point out that from now on the name’s Boffin – Uni Boffin!
Q & As:
Jon, John Lowe Darts and Weight (from the blog before last):
If you have another look at my last blog, Jon, you’ll see that Sigma Pros actually use the yaw component in their impact angle to compensate for inaccuracy caused by lift. This yaw is easier to see in the horizontal plane than in the vertical because there’s no curve of the trajectory due to gravity to confuse things. Sigma Pros are indeed far less forgiving in this regard than the John Lowes, but this is because of the flights/shaft, not because the barrels are longer - switch to the Sigma One flights/shaft with the same barrels and you should find them as or more forgiving than the John Lowes, which is why the Sigma One set-up is recommended for improving players.
Many players do find they throw heavier darts more positively, which does indeed mean they go slightly higher. This is more to do with psychology than physics, however, and I wouldn’t like to speculate about the role of gender in that subject!
John P, UniLab and Barrel Flats:
The reason you get different answers from UniLab Selector and Optimiser for the same STs and SPs, John, is that Selector recommends a darts set-up as sold, ie barrel, shaft and flights. Given the same barrel, Optimiser will then recommend which shaft and flights would be best for you. Because there are so many possible combinations of STs and SPs, these won’t usually be the same as the ones with which it’s sold.
As for the flats on the front of Sigma (and many other) barrels, you’re right that it’s there for strength, which is particularly an issue with higher percentage tungsten. However, Unicorn and I are looking at possible improvements which might help.
Bob and Chris R and Grips:
Take your point about humidity, guys, but that’s what I meant when I talked about “the fine grip disadvantage of possible slipperiness” in my answer to Bob last time. My reference to a possible issue with “variable release” for coarser grips would perhaps have been better expressed as “asymmetric release”, meaning that a rougher finish can make it harder to let go of opposing sides of the barrel exactly simultaneously, which can cause trajectory deviation and yawing. That said, you’re right that “stickiness” can cause a similar problem with fine grips. All in all, as I’ve said before, grip is mostly a matter of personal preference and any future Sigmas might well offer a coarser grip as an alternative to the current fine one.
Keiron and Chris R and Missing is the Missing Word:
Well done to these two and any other Sherlocks who got this – bonus points if you didn’t use Google!